As indicated, the present invention is directed to emulation. However, unlike emulation of central processing units and their associated architectures, the present invention is directed to the emulation of an I/O (input/output) adapter. Accordingly, in order to provide a better description of the present invention, it is useful to have a basic understanding of its background of adapters and the environment in which they are employed. Firstly, therefore, it is important to understand that an adapter, in the data processing sense of the word, is simply a hardware device which is used to communicate between a host (data processing) system and one or more external devices. Thus, an adapter is seen to provide one form of I/O connectivity in a data processing system. More particularly, the present invention is primarily, though not exclusively, directed to what is referred to as the Open System Adapter (OSA), a product offered by the assignee of the present invention. This adapter provides a protocol for data transmission between a host system memory and a data network. Even more particularly, the data network to which the protocol is directed is a LAN (Local Area Network).
The Open System Adapter employs the QDIO protocol. An example of a system that employs this protocol is seen in U.S. Pat. No. 6,976,083 issued to the assignee of the present invention. The QDIO architecture is also described in Volume 46, Numbers 4/5, 2002 of the IBM Journal of Research and Development.
The Open System Adapter couples a host system to a network for I/O transfer in both directions. One of the characteristics of this protocol is that it involves the use of polling. For example, on the host side, polling is undertaken on a periodic basis, say every 10 milliseconds, to see if there is any data to be transferred from the network I/O buffers to the host system memory. Most of the time the polling results in a negative response, meaning that there is no data to be transferred. Likewise, polling is undertaken on the network side to see if there is a request from the host to send data to the network I/O buffer(s). Since most of the time this polling is likely to result in no data being transferred, its elimination is desirable. It is an unexpected result that emulation of the Open System Adapter results in a system and method in which this polling is eliminated without impacting the operation of the Open System Adapter protocol.
Emulation technology is becoming more prevalent in the industry due to the rising cost of hardware development, especially on high end systems. The emulation approach advantageously provides a much lower cost of ownership of the product for pursuing application development. Furthermore, the resurgence of the mainframe class of machine has created an increased desire for code developers to write applications for this type of machine. One of the most significant ones of these high end systems is the zSeries Architecture® of data processor manufactured and marketed by the assignee of the present invention. However, the cost factor for these high end systems is discouraging program writers and designers from working in this area, especially for development and for training purposes. Several vendors now provide zSeries processor emulations that run on either a UnixWare or Linux based workstation. However, included with the processor emulation is the increasing desire to emulate other parts of the system including DASD, coupling, I/O, and networking functions. Queued direct I/O was introduced in 1990. It is a state-of-the-art I/O architecture which provides fast host to LAN communication. With the emulator of the present invention, several changes have been made to enhance the architecture and to improve Queued Direct I/O (QDIO) function on Linux and AIX® platforms. The present application describes Queued Direct I/O enhancements used to perform the Open System Adapter (OSA) function on the zSeries emulation platform.
In order to provide a better description of the present invention, it is useful to have a basic understanding of its background and its environment. Firstly, therefore, it is important to understand that an adapter, in the data processing sense of the word, is simply a hardware device which is used to communicate between a host system and one or more external devices. An adapter thus is seen to provide one form of input/output (I/O) in a data processing system. More particularly, the present invention is primarily, though not exclusively, directed to what is referred to as the Open System Adapter (OSA), a hardware product offered by the assignee of the present invention. This adapter provides a protocol for data transmission between a host system memory and a data network. Even more particularly, the data network to which the protocol is directed is a LAN (Local Area Network).